Super Simple Oscillator + Behringer Crave. Voltage question

[Pateph0n]

Hello everyone.

Quick question here. I’ve put together a couple of super simple oscillators with 2N3904 running on double 9V batteries (18V). I want to use it with my Behringer crave, which operates, according to the manual, at -5/+5 volts. Is it safe to plug the SSO into Behringer’s inputs, or I can potentially ruin my synth?

Only starting out with electronics, so all the voltage stuff is still a little confusing to me.

Thanks for the answer.

[fredrik]

If you check the oscilloscope output in this post:

Getting the SUPER SIMPLE OSCILLATOR to oscillate

The SUPER SIMPLE OSCILLATOR keeps causing headaches, because while it’s a SUPER SIMPLE CIRCUIT (and SUPER CHEAP; the active component costs you a couple of cents) it’s not necessarily a SUPER SIMPLE BUILD, as can be seen in the recurring “oscillator trouble” threads in this forum. So I thought I’d post some suggestions for how to build the oscillator step by step, in a way that will at least tell you if you’ve managed to get it to oscillate. I’ve tested this with a variety of transistors, and h…

you’ll see that the output signal swings between 7.4 V and 10.7 V for the 2N3904 I used there, so while the swing itself is within bounds, there’s a strong DC component – i.e. the output swings around (7.4 + 10.7)/2 = 9 V, not 0 V. You could add a capacitor in series with the output to filter that out, see e.g.

Trouble with the Super Simple Oscillator

The oscillator will swing between the transistor’s breakdown open and close voltages, which will result in a fairly high DC offset; see the oscilloscope picture here for an example: (that specific build swings between 7.4 and 10.7 volts, which corresponds to a DC offset of almost exactly 9 V) Depends on your mixing desk if that’s a problem. If you have an AC coupled input with ok headroom you can just plug it in as is. To filter, you can try anything from, say, 100 nF upwards. Line inputs ar…

(I’d be a bit surprised if you damaged your Crave by feeding in the signal as is, though, but better be safe than sorry, I guess.)

[Pateph0n]

Ok, thanks!

I will mess around with capacitors then. While waiting for the answer I already tried feeding the signal into Crave (couldn’t resist) and it seems fine. I mean it didn’t kill it straight away and it works.

I will still try to adapt the voltage and write back here if I’ll succeed. At the end of the day, I am planning to connect these two together a lot.

[fredrik]

If it works and doesn’t clip, odds are the input is AC coupled (i.e. there’s a capacitor on the way in) but the docs don’t mention anything and I don’t have a Crave here so cannot crack it open and look at the circuitry